This invention relates to an etching end point judging method and to devices suitable for detecting etching processing end points in a plasma discharge process through use of emission spectrometry; and, the invention also relates to an insulation film etching method using the etching end point judging method and the etching processing detection devices. The insulation films include a silicon oxide film (referred to as an oxide film henceforth) and a low-k film consisting of a material having a low dielectric constant.
During dry etching processing of a semiconductor wafer, the emission intensity at a specific wavelength in plasma light changes according to the etching progress of a specific film. A conventional semiconductor wafer etching end point detection method is available to detect changes in the emission intensity at a specific wavelength from plasma and detect an etching end point of a specific film based on the detection result during dry etching processing. In this method, detection errors caused by an irregularity in the detected waveforms due to noise must be prevented. In this regard, methods for improving the detection accuracy of the emission intensity changes are disclosed in Japanese Non-examined Patent Publication No. 61-53728 and No. 63-200533. In Japanese Non-examined Patent Publication No. 61-53728, noise is reduced by a method of moving averages, and in Japanese Non-examined Patent Publication No. 63-200533, noise is reduced by noise square approximation processing.
In an etching end point judging device that judges an etching end point of a wafer which is being processed by etching with a plasma discharge using emission spectrometry, the detection signal becomes weaker after each wafer processing due to attachment of deposits. As described in Japanese Non-examined Patent Publication No. 63-254732, detection signals can be corrected by changing the gain value and offset value of the detection signal for stable etching end point detection. Alternatively, as described in Japanese Non-examined Patent Publication No. 04-57092, without the addition of a gain and offset adjustment function, the detection signal that was fetched to the optical conversion method can be adjusted to a set value for stable etching end point detection.
With the recent progress toward downsizing and high integration of semiconductors, the opening rate (area to be etched) on a semiconductor wafer is becoming smaller and the emission intensity at a specific wavelength that is fetched by a light detector of an optical sensor is becoming weaker. As a result, the level of the sampling signal from a light detector is becoming lower, making it difficult to detect an etching end point correctly based on a sampling signal from the light detector.
As the size of a semiconductor device becomes smaller, the electrical capacity of the silicon oxide film used for insulation between wires increases, and the signal loss between wires can no longer be ignored. As a solution to this problem, a method of reducing the electrical capacity between wires is being developed in which a low dielectric constant material is used as the insulation material between wires. Various materials have been developed as candidates for low dielectric constant materials (referred to as low-k materials henceforth). As described on page 74 in the monthly magazine Semiconductor World, 1998, No. 11, these materials include FSG (k=3.3 to 3.6), HSQ (k=2.9 to 3.1), and Xerogel (k=2.0 or less) as inorganic low-k films, SiLk (k=2.6), BCB (k=2.6), FLARE (k=2.8), and PAE (k=2.8) as organic low-k films, and organic SOG (k=2.8 to 2.9) and HSG (k=2.9).
In addition, a damascene process that enables wiring using copper that has a lower electric resistance than conventional wiring materials is being developed through use of a flattening process (CMP) based on chemical and mechanical corrosion technology.
In the damascene process, the main method is the dual damascene method in which a wiring groove is formed by plasma etching after forming a low-k film, which is used as an insulating material between wires and layers, and then a contact hole is formed between the two layers for permitting electrical connection to the lower layer. The process of the dual damascene method differs depending on whether a contact hole or a groove is etched initially. Currently, various methods are being examined. In either case, grooves and contact holes must be formed on low-k films using plasma etching. By using a process of high precision plasma etching with fewer stages, the yield can be enhanced and the cost can be reduced, thereby substantially enhancing the characteristics of plasma etching (etching process and performance).
However, in the currently manufactured damascene structure, an etching stopper layer is formed by inserting a silicon nitride film on the boundary between the groove and the hole provided on the low-k film. Consequently, the need for a stopper layer formation process and the increase of the dielectric constant of the film due to insertion of a stopper layer become problems. There will be no problem if the dielectric constant of the stopper layer is low. However, to satisfy requirements regarding an etching selection ratio and adherence with the low-k film, a silicon nitride layer is currently being used.
Even if a stopper layer is inserted, the film thickness cannot be increased in terms of an increase of the dielectric constant. Therefore, accurate judgment is necessary regarding whether etching has progressed to the stopper layer. Although the ordinary end point judging system can detect this, more accurate judgment is required. The better method is to employ a structure that does not require insertion of a stopper layer, however, such etching becomes difficult under current conditions.
In an insulating film etching device, a change with the passage of time is detected, such as deterioration of the etching speed, as the etching is repeated. In some cases, the etching may stop. This problem must be solved. In addition, it is important to monitor fluctuations in the etching speed with time for stable operation; however, in the conventional method, the end point judgment time is simply monitored. Moreover, when the etching duration becomes short, such as about 10 seconds, the judgment preparation time and the judgment interval must also be reduced in the end point judgment method. However, in the conventional method, a sufficient measure to address this requirement has not been taken. For an insulation film, as the etched area is often 1% or less, the changes in the plasma emission intensity from the residue that is generated as a result of etching is small. Consequently, an end point judging system that can detect very small changes is necessary. However, a practical system at a reasonable price is not available at present.
To resolve the problem of drift in a lithography position during etching for forming a contact hole on an insulation film, a self-alignment contact technology has been developed. In the end point judgment used in this technology also, since the etched area of the last contact section is small (1% or less), a system having a high detection sensitivity for plasma emission intensity changes is necessary; however, the end point judging system presently available does not satisfy the requirements for high precision and a reasonable cost.
The primary object of this invention is to provide an etching end point judging method and a detection device that are capable of stable detection of etching end points of semiconductor wafers even for a semiconductor wafer having a low opening rate.
The secondary object of this invention is to develop a method of obtaining high-quality etching results by detecting plasma etching end points of semiconductor thin films using an end point judging system that can detect very small changes of plasma emissions and also can measure the data in a short time during plasma processing, in particular, plasma etching processing.
Another object of this invention is to provide an etching end point judging method and a detection device that can eliminate any end point judging detection errors when a pulse type noise is induced in an emission intensity sampling signal (for instance, instantaneous termination of discharge power or an abnormality caused by modulation of the emission intensity due to a sudden change of the plasma state caused by an instability).
Another object of this invention is to provide an etching end point judging method and a detection device that can easily display occurrences of plasma discharge abnormalities as history data.
Another object of this invention is to provide an etching method for enabling high-precision etching in a damascene process and a self-alignment process using a method or system that can measure, with a high precision, end points of an insulation film etching process of a semiconductor device.
Another object of this invention is to prevent etching faults in an etching device, which are caused by changes in time, by determining the etching speed through measurement of the etching time required to etch up to the stopper layer in the damascene process or up to the insulation film on the gate in the self-alignment contact process, and monitoring the fluctuations. By judging the correct time required for reaching the stopper layer in the damascene process, corrosion of a thin silicon nitride layer can be retarded, thereby improving the real selection ratio.
Another object of this invention is to control deterioration of device performance by retarding excessive advancement of etching on the bedding layer by judging the correct etching ending time, since etching ends in a short time, in the process for removing the silicon nitride layer that was formed on the bedding in a damascene process or a self-alignment contact process.
An object of this invention is to provide an etching end point judging method for use in dry etching. The method includes a step of reducing noise by processing input signal waveforms through a first digital filter, a step of finding a differential coefficient (primary or secondary) of a signal waveform through differential processing, a step of obtaining a smoothed differential coefficient value by reducing the noise component of the time series differential coefficient that was obtained by the previous step, and a step of judging an etching end point by comparing the smoothed differential coefficient value and a preset value through discrimination.
Another object of this invention is to provide an etching end point judging method for judging an etching end point from time series data of an emission intensity differential coefficient. The method includes a step of displaying a transition of time series data of the differential coefficient through a display method and adding the display indicating an abnormality on the display of the time series data of the differential coefficient when an abnormality is detected.
Another object of this invention is to provide an etching end point judging device that uses emission spectrometry. The device is equipped with an AD converter for obtaining emission intensity time series data of a specific wavelength, a first digital filtering device for performing smoothing processing for the time series data, a differential operation device for obtaining a differential coefficient of the smoothed time series data, a second digital filtering device for performing smoothing processing for the time series data of the differential coefficient that was calculated, and a discrimination device for judging an etching end point by comparing the smoothing differential coefficient value and a preset value.
Another object of this invention is to provide an insulation film etching method for judging an etching end point using the etching end point judging method described above in the etching of an insulation film containing a low-k film consisting of a silicon oxide film or a low dielectric constant material.
This invention can provide a very stable method for judging etching processing end points, since it enables accurate calculation of emission intensity changes. In addition, in end point judgment that includes differential coefficient calculation processing, noise in the sampling signals from a light detector can be reduced effectively by setting digital filtering processing before and after differential coefficient calculation processing, enabling stable and accurate end point judgment.
By setting coefficient correction processing in digital filtering processing in the former stage, differential coefficient calculation processing, and digital filtering processing of the latter stage, noise of sampling signals from a light detector can be reduced effectively in the case of an abnormality occurring during the etching processing, enabling stable and accurate end point judgment.
By drawing in a zero or the preset display position with a specific color arrangement when an etching processing abnormality occurs during differential coefficient display, a high-quality device that facilitates abnormality monitoring during etching processing can be provided.
This invention enables execution of a correct end point judgment, thereby providing the effect of setting a lower over-etching than obtainable with time management etching. As a result, excessive corrosion of the bedding layer can be controlled. Since this invention reduces the over-etching duration, improvement of the throughput can be expected. Since changes in the passage of the etching time can be monitored, an etching device abnormality can be detected at an early stage, enabling prevention of a large number of etching faults.
This invention enables determination of a correct sense voltage value for the target output value of a photo-multiplier by using a sense voltage value for a target output voltage value of a photo-multiplier through a relational expression. Therefore, even for a semiconductor wafer having a small opening rate, the etching signals used for stable detection of etching end points of semiconductor wafers can be controlled to a specified value repeatedly without any irregularity between wafers.
By using the end point judging system of this invention, judgment can be prepared in a short time and small plasma emission intensity changes can be detected. Therefore, this system can be applied to end point judgment of insulation film etching of a small etched area.